1. Field of the Invention
The present invention relates to an image display system, an image display apparatus, and a control method for an image display apparatus, in which a video signal is displayed by converting the frame rate thereof.
2. Description of the Related Art
When appreciating on a television set a picture photographed by a digital camera (photographed image), a partial region (cut-out region) of the photographed image may be cut out and displayed on the full screen of the television set. At this time, the cut-out position (the position of the region cutout from the photographed image) may be moved by a cursor key of a digital camera main body, etc., so that various regions in the photographed image can be appreciated.
In addition, a partial region of the photographed image can be cut out and printed on paper, etc. At this time, in order to check the cut-out region, the television set can be connected to a printer so that the cut-out region can be displayed on the full screen of the television set. Even in such a case, the cut-out position can be moved by a cursor key of the printer, etc., so that a region to be printed is determined.
On the other hand, some television sets perform frame rate conversion (FRC) for the purpose of a flicker countermeasure or the improvement of animation response. For example, the FRC detects a motion vector from frame images being inputted, creates an interpolated frame by the use of the detected motion vector, and converts the frame rate thereof from 60 Hz into 120 Hz.
In cases where the digital camera and the television set are connected to each other, or in cases where the printer and the television set are connected to each other, a video signal of a photographed image is inputted to the television set at a frame rate of 60 Hz. The television set creates interpolated frames from the video signal that is inputted at 60 Hz, and displays the video signal at a frame rate of 120 Hz. When a user moves the position of the cut-out region by means of a cursor key or the like, it becomes difficult to detect a motion vector because the moving speed (motion in the video displayed on the television set) of the cut-out position is generally fast. At this time, there has been a problem that when an interpolated frame is created by using an incorrect motion vector, an image of the interpolated frame is disturbed (a disturbance such as noise occurs in the video being currently appreciated). Here, note that the movement of the position of a cut-out region is equivalent to the change of a region to be cut.
A conventional technology in view of such a problem is disclosed in Japanese patent application laid-open No. H07-162811, for example. Specifically, in a method disclosed in Japanese patent application laid-open No. H07-162811, the same image as that of an original frame is used as an interpolated frame in a region in which the detection of a motion vector is difficult because the moving speed of a video being displayed is fast. Then, the disturbance of an image is blurred by applying an LPF (low pass filter) to the interpolated frame created in this manner.